Early cochlear implantation supports narrative skills of children with prelingual single-sided deafness

Prelingual single-sided deafness (SSD) not only affects children’s hearing skills, but can also lead to speech-language delays and academic underachievement. Early cochlear implantation leads to improved spatial hearing, but the impact on language development is less studied. In our longitudinal study, we assessed the language skills of young children with SSD and a cochlear implant (CI). In particular, we investigated their narrative skills in comparison to two control groups: children with SSD without a CI, and children with bilateral normal hearing. We found that children with SSD and a CI performed in line with their normal-hearing peers with regard to narrative and verbal short-term memory skills. Children with SSD without a CI had worse narrative (group difference = − 0.67, p = 0.02) and verbal short-term memory (group difference = − 0.68, p = 0.03) scores than the implanted group. Verbal short-term memory scores and grammar scores each correlated positively with narrative scores across all groups. Early grammar scores (at 2–3 years of age) could partially predict later narrative scores (at 4–6 years of age). These results show that young children with prelingual SSD can benefit from early cochlear implantation to achieve age-appropriate language skills. They support the provision of a CI to children with prelingual SSD.


Part 2: Supplementary Analyses for grammar
Most of the grammar scores of the current participants have been discussed elsewhere (Arras et al., 2021).Therefore, they were not the focus of the current work.However, we did want to discuss the connection between early and later grammar scores on the one hand and narrative skills on the other hand.In this supplementary analysis, we provide more detail about the grammar scores as a separate outcome measure.

Longitudinal grammar scores
Longitudinal grammar data were available for 66 children, aged 2 to 6.6 years, across 292 assessments: 18 children in the SSD+CI group (mean age 3.6 ± 1.1 years), 16 children in the SSD group (mean age 3.6 ± 1.0 years), and 32 children in the NH group (mean age 3.9 ± 1.3 years).The age-corrected test scores quantified the children's grammar scores and followed a normal distribution (W = 1.00, p = 0.73).The mean score was 0.34 in the SSD+CI group, -0.16 in the SSD group, and 0.45 in the NH group.
Scores were significantly different across groups (X² = 6.57, p = 0.04), but the post-hoc contrasts were not significant after Bonferroni correction.Maternal education level was a significant predictor as well (X² = 4.90, p = 0.03), with children from mothers with higher education achieving higher grammar scores than their peers (0.47, p = 0.03).The model explained more than half of the variance (R²m = 0.11, R²c = 0.59), and the residual variances were similar across groups (F = 0.39, p = 0.68) and maternal education levels (F = 0.65, p = 0.42).The grammar scores are compared across groups (left) and maternal education levels (right) in Supplementary Fig. S5.Individual developmental trajectories for all children with SSD, compared to the mean of the NH group, are presented in Supplementary Fig. S6.
Supplementary Figure S5: Individual standardized scores for the grammar test, compared across groups (a) and maternal education levels (b).The error bars represent the estimated marginal mean and corresponding standard deviation for each group.
Supplementary Figure S6: Individual developmental trajectories of children with SSD for grammar, separated for the SSD+CI group (left) and the SSD group (right).The average score and standard deviation of the NH group for each age 6-month interval is shown in black.The dotted lines at +1 and -1 mark the cut-offs for the age-referenced "average" scores.

Early grammar scores
The subset of early grammar data, with scores of 54 children aged 2 to 3.7 years, spanned 156 assessments.This subset contained data for 18 children in the SSD+CI group (mean age 2.8 ± 0.5 years), 15 children in the SSD group (mean age 2.9 ± 0.5 years), and 21 children in the NH group (mean age 2.7 ± 0.5 years).Age-corrected test scores followed a normal distribution (W = 0.99, p = 0.31).The mean score was 0.33 in the SSD+CI group, -0.18 in the SSD group, and 0.52 in the NH group.
Scores were significantly different across groups (X² = 12.69, p = 0.002), with worse scores for the children with SSD compared to the NH control group (-0.67, p = 0.003).The children with SSD and a CI outperformed their non-implanted peers (0.51, p = 0.04) and achieved scores similar to those of the NH group.The model explained more than half of the variance (R²m = 0.14, R²c = 0.60), and the residual variances were similar across groups (F = 2.34, p = 0.10).The grammar scores for the three groups are compared in Supplementary Fig. S7.
As expected, these findings match our earlier report, which was based on (largely) the same dataset.